PVC pipe is measured by the inside diameter of the pipe so that the volume of air or liquid can be measured. The inside diameter of the Sonostar hubs corresponds to the outside diameter of the pipe so that the pipe can fit snugly inside the hub arms. The actual inside diameter of standard Sonostar hubs is .84 of an inch.
Each arm has exactly one inch of sleeve room for the inserted pipe. You have the option of either gluing the pipes into the hubs or securing them with nuts and bolts. Stainless Steel nuts and bolts are included in both the Basic Kits and the Full Kits.